The present invention relates to an assembly and a method for spinal fixation, and in particular relates to a spinal rod and a method for spinal fixation configured to reduce the use of bone penetrating connections and/or additional fixture devices.
Spinal rods are routinely used in spinal fusion procedures to treat different spinal disorders, such as scoliosis, degenerative disc disease, disc herniation, spinal stenosis, or other abnormalities. Typically, such procedures involve properly aligning two or more vertebrae and permanently fusing them together through the use of two or more pedicle screws attached by the spinal rods. This construct stabilizes the spine until fusion occurs.
Spinal rod fracture is the most common type of fixation device failure in spinal fusion procedures. Particularly in procedures such as corrective osteotomy and long-segment spinal fusion, the risk of spinal rod failure can be significant. Spinal rod fractures occur because the implanted spinal rod is unable to sustain the load long enough to allow the vertebrae to fuse together. Rod failure generally does not occur over a single overloading event (shock loading), but instead occurs due to fatigue over time. To prevent spinal rod failure, multiple spinal rods across the same vertebral bodies may be required. For example, when a single spinal rod is unable to provide the necessary support, multiple rods across the same vertebral bodies may be connected with additional bone anchoring pedicle screws to provide additional rigidity.
A “quad rod” technique uses four rods instead of two rods across the vertebrae. A second rod is added to the main rod on each side of the spinous process and connected by rod-to-rod connectors to increase overall rigidity of the fixation assembly. However, the quad rod technique requires multiple rod-to-rod connectors to connect the first and second rod to each other, which further complicates the spinal fusion surgery by adding additional surgery time and effort to locate and place connectors in narrow regions between screws and rods. Furthermore, the rod-to-rod connector connections at the spinal rod represent the weakest point of the spinal rod, and hence the area most susceptible to structural failure. The greater amount of connection points lead to more potential rod failure points. Additional rod interfaces, and rod-to-rod connectors may exacerbate the risk of stress related failure.
Therefore, there exists a need to provide a spinal fixation assembly and method that provides rigidity without requiring additional fixture devices.